Generally, I participate in Zen sesshins (7-day meditation retreats) four times a year. Typically, I find that it takes 3-4 days before my meditation becomes fully energized. Initially, my mind is much more easily distracted by thoughts. By the fifth or sixth day, it feels like my meditation is more single-pointed and solid. In order to investigate this phenomenon empirically, over the course of a 7-day sesshin at Tahoma Zen Monastery in February, 2015, I recorded 20-minute meditation periods at the end of each day, around 10:30 pm after the conclusion of formal zazen practice periods.
The following graphs show relative band power median values recorded at the four sensors of the Muse headband: lb (left back TP9), lf (left front FP1), rf (right front FP2), and rb (right back TP10). During the first ten minutes I sat with eyes open, zazen style, and the last ten minutes with eyes closed. The data displayed below are for 400 seconds in the middle of zazen. Error bars are indicated for one standard deviation.
It’s interesting to note that in the two sensors near the ears (left back and right back), the alpha component stayed strong and relatively unchanged over the course of the seven days. But at the front of the head (left front and right front), alpha power seemed to drop off toward the end of the sesshin while beta and gamma both increased. On the seventh day, especially, the higher frequency bands seem to dominate over the lower frequency bands alpha, theta and delta.